Lyman a emission

A number of schemes are available for observing optical resonance in the trap. A straightforward technique is to quench the 2S state with a small electric field (or possibly by collisional quenching) and observe the Lyman-a emission. Most of the quenched atoms will escape from the trap, but the loss rate is so small that its effect on the density would be negligible. 

It was found by Warneck17 and by Okabe16 that 10% H2 in argon at a total pressure of 1 mm. gave an intense (>1014 quanta/sec.) almost pure Lyman a emission (1216 A.). Attempts to produce N atom and O atom resonance lines by similar techniques were unsuccessful, but some photo-chemically useful line groups at 1493-95 and 1743-45 A. were observed in the case of nitrogen. 

Figure 7.28 Fano lineshape in H2. The predissociation of the N=2 [R(l) line] and N=1 [R(0) line] levels of the D1ri,ie(u = 5) state by the continuum of B 1is detected by monitoring the Lyman-a emission from one of the fragment atoms. The dots represent the lineshape calculated from the Fano formula [Eq. (7.9.1)] with parameter values Y(N = 2) = 14.5 cm 1,g(N = 2) = -9 r(jV = 1) = 4.8 cm 1,q(N = 1) = —18. These lineshapes should be compared to the symmetric profile of Fig. 7.16 (q = 00). The horizontal dotted line separates the interacting continuum Oi from the noninteracting continua [

FIGURE 13 Objective-grating far-UV spectrum of Comet Halley, obtained by the Naval Research Laboratory in a 1986 sounding rocket flight, which excludes the hydrogen Lyman a emission. The spectrum reveals far-UV emissions of atomic oxygen, carbon, sulfur, and also carbon monoxide (CO) (unlabeled features between the OI and CI features). 

Fig. 12.5. Parts of the spectra of two QSOs (with emission redshifts 2.9 and 3.3 respectively) taken with the 4-m William Herschel Telescope on La Palma with a resolution of about 50kms 1 showing Lyman-a lines with damping wings (column densities N(H i) 2 x 1021 cm 2 or 6M0pc-2 and 8 x 1020 cm-2 or 2.4 Mq pc-2 respectively). After Pettini et al. (1997).

Fig. 12.9. Composite spectrum of Lyman-break galaxies showing a combination of interstellar and stellar absorption lines, P Cygni features and nebular emission lines, dominated by Lyman-a. After Shapley et al. (2003).

Extremely stringent lower limits were reported by Rank (29) in 1968. A spectroscopic detection of the Lyman a(2 p - 1 s) emission line of the quarkonium atom (u-quark plus electron) at 2733 A was expected to be able to show less than 3 108 positive quarks, to be compared with 1010 lithium atoms detected by 2 p - 2 s emission at 6708 A. With certain assumptions (the reader is referred to the original article), less than one quark was found per 1018 nucleons in sea water and 1017 nucleons in seaweed, plankton and oysters. Classical oil-drop experiments (with four kinds of oil light mineral, soya-bean, peanut and cod-liver) were interpreted as less than one quark per 1020 nucleons. Whereas a recent value (18) for deep ocean sediments was below 10 21 per nucleon, much more severe limits were reported (30) in 1966 for sea water (quark/nucleon ratio below 3 10-29) and air (below 5 10-27) with certain assumptions about concentration before entrance in the mass spectrometer. At the same time, the ratio was shown to be below 10 17 for a meteorite. Cook etal. (31) attempted to concentrate quarks by ion-exchange columns in aqueous solution, assuming a position of elution between Na+ and Li+. As discussed in the next section, cations with charge + 2/3 may be more similar to Cs+. Anyhow, values below 10 23 for the quark to nucleon ratio were found for several rocks (e.g., volcanic lava) and minerals. It is clear that if such values below a quark per gramme are accurate, we have a very hard time to find the object but it needs a considerably sophisticated technique to be certain that available quarks are not lost before detection. 

When A and B are identical atomic species (e.g., H + -H259 or He+-He260), radiative emissions may result from neutral target excitation as well as from electron capture by the ionic projectile into the same excited state. Both processes yield Lyman a radiation in the case of H+-H collisions,259... 

Fig. 8.12. A possible scenario for trapped antihydrogen spectroscopy. The microwaves quench the 28 antihydrogen via the 2P3/2 state, which spontaneously decays by emission of a Lyman-a photon.

The technique for studying the 2S1/2 2P3/2 transitions in Si13+ by laser spectroscopy is illustrated in Fig. 1. Laser radiation at 734 nm is used to excite ions from the metastable 2S]y2 state to the 2P3/2 state, from which they rapidly decay to the ground state via an allowed electric dipole transition. The resonance is monitored by observing the rate of emission of 2 keV Lyman-a X-ray photons as a function of the laser frequency. The 2S Lamb shift may be deduced from such a measurement of the 2S1/2-ZP3/2 interval because the n = 2 fine structure splitting is more accurately known theoretically. 

Measurement of the Radiative Decay Rate of Ps in the 23Pt (J = 0.1,21 States The radiative decay rate 7 of 23Pj Ps was measured as a byproduct of an experiment [21] to determine the frequency intervals Vj between the 23Sj and 23Pj states (J=0,l,2). The 23Pj states decay to the l3Si state by emission of a Lyman-a photon at 243 nm. To lowest order in a, the expected decay rate... 

OGO-5, a few other emissions could be identified (Fig. 4). The OH-emissions at 3090 A which are just barely visible also from the ground turned out to be the strongest lines besides the Lyman a line, and for the first time production rates for this radical could be derived and compared with those for neutral hydrogen. A description of the method by which production rates can be derived from the observed line intensities is e.g. given by KeUer These calculations require the assumption of a certain coma model. The results from several recent comets favor the interpretation that the observed hydrogen and hydroxyl have been formed by dissociation of water. This is roughly demonstrated by the abundances of H and OH given in Table 2. In the case of HjO dissociation one should expect about twice as many H atoms ls OH... 

Fig. 5. The T Tauri-phase fluxes (top) compared to present solar fluxes (Ackermann, 1971) for ultraviolet and visual wavelengths. The strong emission lines of Lyman-a (1215 A), Mgll (2800 A) and Balmer-a (6563 A) can be seen in the T Tauri spectrum. Fluxes have been reduced to those intercepted at a distance of 1 AU from the star.

In the spectral region near 120 nm, the solar hydrogen emission line at Lyman a represents an important source of ionization and dissociation. During quiet periods, it contains more energy than the rest of the spectrum at shorter wavelengths. The total flux of this line as well as its shape vary with solar activity. The actinic flux varies between a minimum of about 3.0 x 1011 photons cm 2s 1 for quiet solar activity and a maximum of about 6.0 x 1011 during high solar activity. 

Most of the intensity of this emission spectrum lies within the (0,0,0)-(0, O, O) band centred at 760 nm and thus it is necessary to utilize a photomultipher with an S20 (or SI) or similar cathode for intensity measurements. The e.p.r. signal or absorption of Lyman-a resonance radiation at 121 6 nm H( P - S) are other end-point indicators which have been used. The NO titration method is invaUd in the presence of large concentrations of H2 unless an extremely rapid flow velocity is used, since the reaction ... 

Unfortunately, two-photon excitation of hydrogen 1S-2S requires ultraviolet radiation near 243 nm, where there are still no good cw sources available. The best spectra so far have been recorded by C. Wieman, (39) who used a cw dye laser near 486 nm followed by a pulsed dye laser amplifier and a crystal frequency doubler. Discharge-produced hydrogen atoms were excited with a standing wave field from this source, and the signal was detected by monitoring the collision-induced emission of vacuum ultraviolet Lyman-a photons. 

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